Network-assisted direct device to device (D2D) communication is expected to be a key feature supported by next generation cellular communication networks. FIG. 1 illustrates a cellular communication network 10 that enables direct D2D communications. As illustrated, the cellular communication network 10 includes a base station (BS) 12 that serves a corresponding cell 14 of the cellular communication network 10. While only one base station 12 is illustrated, the cellular communication network 10 includes numerous base stations 12 serving corresponding cells 14. In this example, wireless devices (WDs) 16, 18, and 20 are located within the cell 14. The wireless devices 16 and 18 are in proximity to one another. As such, when the wireless devices 16 and 18 desire to establish a bearer link, rather than establishing the bearer link through the base station 12, the cellular communication network 10 assists the wireless devices 16 and 18 to establish a direct D2D communication link (i.e., a direct D2D bearer link) between one another. More specifically, through signaling with the base station 12 or some other mechanism, the wireless devices 16 and 18 discover one another using a D2D device discovery process and then establish a D2D communication link directly between one another rather than through the base station 12.
Direct D2D communication is possible regardless of whether the cellular communication network 10 is Frequency Division Duplex (FDD) (i.e., uses different uplink and downlink frequency bands) or Time Division Duplex (TDD) (i.e., using the same frequency band but different time slots for uplink and downlink). However, it is commonly accepted that a direct D2D communication link, such as that established between the wireless devices 16 and 18, is preferably a TDD communication link where transmissions by one wireless device use the same resources as reception by the other wireless device. These “resources” are physical frequency and/or time resources depending on the particular implementation of the cellular communication network 10. TDD (i.e., half duplex operation) is preferred because operating a transmitter and receiver in the same frequency band in a half duplex fashion is easier to implement than a full duplex FDD implementation.
In order to provide spectral efficiency, it is preferable for the D2D communication link to use the same resources as those used by the cellular communication network 10, in which case the cellular communication network 10 performs actions such as mode selection, network-controlled scheduling, and power control. In this example, the D2D communication link uses either an uplink resource or a downlink resource of the cellular communication network 10 that is also assigned to the wireless device 20. While using the same resources as the cellular communication network 10 provides spectral efficiency, doing so also gives rise to new intra-cell and inter-cell interference situations. For example, due to the presence of D2D communication links and the sharing of resources, intra-cell orthogonality is no longer maintained.
Specifically, FIG. 2 illustrates both intra-cell and inter-cell interference caused by transmissions between the wireless devices 16 and 18 over the D2D communication link when using a downlink (DL) resource of the cellular communication network 10. The transmissions between the wireless devices 16 and 18 over the D2D communication link using the DL resource cause strong intra-cell interference to the wireless device 20 located within the cell 14 that uses the same DL resource. In addition, the transmissions between the wireless devices 16 and 18 over the D2D communication link using the DL resource cause strong interference to wireless devices that use the same DL resource in neighboring cells. For example, the transmissions between the wireless devices 16 and 18 over the D2D communication link using the DL resource cause strong interference to a wireless device 22 located in a neighboring cell 24 served by a neighboring base station 26. In addition, while not illustrated, transmissions between the wireless devices 16 and 18 over the D2D communication link using the DL resource may cause interference to other wireless devices in the cell 14 and/or in neighboring cells such as the neighboring cell 24.
FIG. 3 illustrates both intra-cell and inter-cell interference when the D2D communication link between the wireless devices 16 and 18 uses an uplink (UL) resource of the cellular communication network 10. As illustrated, when the wireless device 16 transmits to the wireless device 18 over the D2D communication link using the UL resource, uplink transmissions by the wireless device 20 using the same UL resource cause strong intra-cell interference to the wireless device 18 when receiving the transmissions from the wireless device 16 over the D2D communication link. Similarly, uplink transmissions from the wireless device 22 to the neighboring base station 26 in the neighboring cell 24 using the same UL resource cause strong inter-cell interference to the wireless device 18 when receiving the transmissions from the wireless device 16 over the D2D communication link. In addition, while not illustrated, transmissions between the wireless devices 16 and 18 over the D2D communication link using the DL resource may cause interference to the uplinks from other wireless devices to the base station 12 in the cell 14 and/or base stations in neighboring cells such as the neighboring base station 26 in the neighboring cell 24.
Thus, D2D communication using the same resources used for downlinks and uplinks in the cellular communication network 10 results in new interference scenarios not envisioned in conventional cellular communication networks. As such, there is a need for systems and methods for minimizing, or at least substantially reducing, interference resulting from D2D communication in a cellular communication network.